Methods and apparatus for compressing material during additive manufacturing

ABSTRACT

An additive manufacturing device and method for delivering a flowable material from a nozzle of a programmable computer numeric control (CNC) machine, and compressing the flowable material with a compression roller. In one embodiment, the device includes a nozzle configured to deposit a flowable material on a surface; and a roller configured to compress the deposited flowable material, wherein the roller comprises: a flat center portion having a constant diameter; and opposed end portions, wherein each end portion extends outwardly from the flat center portion, and wherein a radially outermost surface of each end portion is angled relative a rotational axis of the roller.

TECHNICAL FIELD

Aspects of the present disclosure relate to apparatus and methods forfabricating components. In some instances, aspects of the presentdisclosure relate to apparatus and methods for fabricating components(such as, e.g., automobile parts, medical devices, machine components,consumer products, etc.) via additive manufacturing techniques orprocesses, such as, e.g., 3D printing manufacturing techniques orprocesses.

BACKGROUND

Additive manufacturing techniques and processes generally involve thebuildup of one or more materials to make a net or near net shape (NNS)object, in contrast to subtractive manufacturing methods. Though“additive manufacturing” is an industry standard term (ASTM F2792),additive manufacturing encompasses various manufacturing and prototypingtechniques known under a variety of names, including freeformfabrication, 3D printing, rapid prototyping/tooling, etc. Additivemanufacturing techniques are capable of fabricating complex componentsfrom a wide variety of materials. Generally, a freestanding object canbe fabricated from a computer-aided design (CAD) model.

One such process, commonly referred to as Fused Deposition Modeling(FDM), comprises a process of melting a very thin layer of a flowablematerial (e.g., a thermoplastic material), and applying this material inlayers to produce a final part. This is commonly accomplished by passinga continuous thin filament of thermoplastic material through a heatednozzle, which melts the thermoplastic material and applies it to thestructure being printed. The heated material then is applied to theexisting structure in thin layers, melting and fusing with the existingmaterial to produce a solid finished product.

A common method of additive manufacturing, or 3D printing, generallyincludes forming and extruding a bead of flowable material (e.g., moltenthermoplastic), applying the bead of material in a strata of layers toform a facsimile of an article, and machining such facsimile to producean end product. Such a process is generally achieved by means of anextruder mounted on a computer numeric controlled (CNC) machine withcontrolled motion along at least the X, Y, and Z-axes. In some cases,the flowable material, such as, e.g., molten thermoplastic material, maybe infused with a reinforcing material (e.g., strands of fiber) toenhance the material's strength.

The flowable material, while generally hot and pliable, may be depositedupon a substrate (e.g., a mold), pressed down or otherwise flattened tosome extent, and leveled to a consistent thickness, preferably by meansof a tangentially compensated roller mechanism. The flattening processmay aid in fusing a new layer of the flowable material to the previouslydeposited layer of the flowable material. In some instances, anoscillating plate may be used to flatten the bead of flowable materialto a desired thickness, thus effecting fusion to the previouslydeposited layer of flowable material. The deposition process may berepeated so that each successive layer of flowable material is depositedupon an existing layer to build up and manufacture a desired componentstructure. When executed properly, the new layer of flowable materialmay be deposited at a temperature sufficient enough to allow a new layerof such material to melt and fuse with a previously deposited layer,thus producing a solid part.

The process of 3D-printing a part, which utilizes a large print bead toachieve an accurate final size and shape, requires a two-step process.This two-step process, commonly referred to as near-net-shape, begins byprinting a part to a size slightly larger than needed, then machining,milling or routing the part to the final size and shape. The additionaltime required to trim the part to final size is more than compensatedfor by the much faster printing process.

In the practice of the aforementioned process, a major deficiency hasbeen noted. In creating parts with successive layers, the layers must beapplied in uniform, smooth beads with no trapped air between layers. Inapplying a successive layer of material upon an existing layer, theexisting layer must be leveled smoothly in order to effectively bondwith the successive layer. The successive layer of material has to beleveled smoothly and trapped air must be pressed out between the layers.The layers must be of uniform width, height, and shape, in order toproduce consistent parts. Also, the flattening device must be able tonavigate corners without gouging in, or dragging the flowable material.Smooth layers allow for better bonding between layers, resulting inbetter strength characteristics in the finished part. Uniform layersallow for consistent bonding of layers, plus less machining time inorder to get a smooth part. Air in or between layers can cause voids inthe part when machined, which can weaken the bond, and render the partunusable.

In past attempts to address the aforementioned concerns, a number ofdifferent methods have been attempted. One such attempted methodinvolves the use of an oscillating plate for tamping the bead to achieveboth leveling and bonding. Such a device, however, does not create asmooth bead of uniform width, and therefore requires extra machining,among other problems. While the use of a roller is the preferred methodfor achieving a smooth and well-bonded strata of layers, attempts by theprior art to employ such a method have resulted in unsatisfactoryresults.

Another method that has been employed is the use of a grooved roller. Agrooved roller, however, does not create a smooth bead, nor does itremove the trapped air between the layers. Attempts to employ a smooth,straight roller have been met with some success; however this method haslikewise given rise to unsatisfactory results. The desired compressionroller must be somewhat wider than the final compressed surface of thedeposited layer that it is flattening. This is due to a number offactors intrinsic to the process, including coverage requirements whennegotiating curves and corners in the deposition process.

Another inherent characteristic of the additive manufacturing process isthe slight decompression of the deposited layer, which occursimmediately after the compression roller passes over the bead of moltenmaterial. Such action results in the surface of the final flattenedlayer rising up, and remaining slightly higher than the bottom of thecompression roller. When an applicator head rotates to execute a changein tool-path direction, the edges, as well as the outer regions of theroller tend to engage the surface of the final flattened layer, since itis slightly higher than the bottom of the roller, resulting in theroller gouging and dragging the deposited material during thetransition. A similar problem occurs when depositing a layer adjacent toa previously deposited layer. In such a case, the existing layer isagain, slightly higher than the bottom of the roller, the result ofwhich is the same type of problem encountered during directionaltransition. It is therefore desirable to provide a compression roller ofa design that will eliminate, or greatly mitigate the negative aspectsof a typical, straight cylindrical roller.

SUMMARY

Aspects of the present disclosure relate to, among other things, methodsand apparatus for fabricating components via additive manufacturing,such as, e.g., 3D printing techniques. Each of the aspects disclosedherein may include one or more of the features described in connectionwith any of the other disclosed aspects. In one aspect, the disclosuredescribes, among other things, a compression roller that can flatten andlevel layers of molten material in the additive manufacturing process,without gouging into, or dragging the previously-deposited material.

The description below provides a compression roller with a flat centerportion for engaging and flattening the deposited bead, with the outerextremities of said roller gradually tapering to the ends in a slightelliptical curve. The flat surface of such a roller provides smoothcompression and bonding of the deposited material layer, while thegradually-curved outer surface facilitates destruction-free trackingalong curved portions of the deposited layer, as well as duringdirectional changes in the tool path.

In one example, the additive manufacturing device comprises a nozzleconfigured to deposit a flowable material on a surface; and a rollerconfigured to compress the deposited flowable material, wherein theroller comprises: a flat center portion having a constant diameter; andopposed end portions, wherein each end portion extends outwardly fromthe flat center portion, and wherein a radially outermost surface ofeach end portion is angled relative a rotational axis of the roller.

In another example, the additive manufacturing device comprises a nozzleconfigured to deposit a flowable material; and a roller configured tocompress the deposited flowable material, wherein the roller comprises:a cylindrical center portion having a first diameter; and opposed firstand second end portions having second and third diameters respectively,wherein the first and second end portions extend from the centerportion, and wherein the first diameter is greater than the second andthird diameters.

In another aspect, the present disclosure is directed to an additivemanufacturing method for compressing a flowable material with acompression roller. In one embodiment, the method comprising depositinga layer of a flowable material on to a surface; and compressing thelayer of the flowable material with a roller, wherein the rollercomprises: a flat center portion having a constant diameter; and opposedend portions, wherein each end portion extends outwardly from the centerportion, and wherein a radially outermost surface of each end portion isangled relative a rotational axis of the roller.

As used herein, the terms “comprises,” “comprising,” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchas a process, method, article, or apparatus. The term “exemplary” isused in the sense of “example,” rather than “ideal.”

It may be understood that both the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not restrictive of the disclosure, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate exemplary aspects of the presentdisclosure and together with the description, serve to explain theprinciples of the disclosure.

FIG. 1 is a perspective view of an exemplary CNC machine operablepursuant to an additive manufacturing process to form articles,according to an aspect of the present disclosure;

FIG. 2 is an enlarged perspective view of an exemplary carrier andapplicator assembly of the exemplary CNC machine shown in FIG. 1;

FIG. 3 is an enlarged cross-sectional view of an exemplary applicatorhead assembly shown in FIG. 2;

FIG. 4 is an enlarged cross-sectional view of an exemplary depositionhead and compression roller assembly, illustrating the slightdecompression of a deposited layer, which occurs immediately after thecompression roller passes over the deposited bead of molten material;

FIG. 5a is an enlarged plan view of an exemplary carrier and applicatorassembly of the exemplary CNC additive manufacturing machine shown inFIG. 1;

FIG. 5b is an enlarged plan view of an exemplary bead compressionroller, illustrating the different surface features of the roller;

FIG. 6a is an enlarged cross-sectional view of an exemplary compressionroller, with an elliptically tapered outer surface feature, compressinga molten material bead alongside a previously-deposited and compressedlayer of material; and

FIG. 6b is an enlarged cross-sectional perspective view of an exemplarymaterial compression roller, with an elliptically tapered outer surfacefeature, executing a tool-path directional change.

DETAIL DESCRIPTION OF THE INVENTION

The present disclosure is drawn to, among other things, methods andapparatus for fabricating multiple components via additive manufacturingtechniques, such as, e.g., 3D printing. More particularly, the methodsand apparatus described herein comprise a method and apparatus foreliminating, or otherwise substantially reducing damage to the surfaceof deposited and compressed molten material bead(s) during thestratification process of additive manufacturing by, e.g., providing acompression roller that can flatten and level layers of molten materialin the additive manufacturing process, without gouging into, or draggingthe previously-deposited material.

For purposes of brevity, the methods and apparatus described herein willbe discussed in connection with fabricating parts from thermoplasticmaterials. However, those of ordinary skill in the art will readilyrecognize that the disclosed apparatus and methods may be used with anyflowable material suitable for additive manufacturing, such as, e.g., 3Dprinting.

In one aspect, the present disclosure is directed to an extruder-based3D printing head including a compression roller having a shape thatfacilitates compressing a bead of flowable material (e.g., athermoplastic material) by eliminating distortion of the layered andcompressed surface. With reference now to FIG. 1 of the drawings, thereis illustrated a programmable computer numeric control (CNC) machine 1embodying aspects of the present disclosure. A controller (not shown)may be operatively connected to machine 1 for displacing an applicationnozzle along a longitudinal line of travel or x-axis, a transverse lineof travel or a y-axis, and a vertical line of travel or z-axis, inaccordance with a program inputted or loaded into the controller forperforming an additive manufacturing process to replicate a desiredcomponent. CNC machine 1 may be configured to print or otherwise build3D parts from digital representations of the 3D parts (e.g., AMF and STLformat files) programmed into the controller. For example, in anextrusion-based additive manufacturing system, a 3D part may be printedfrom a digital representation of the 3D part in a layer-by-layer mannerby extruding a flowable material. The flowable material may be extrudedthrough an extrusion tip carried by a print head of the system, and isdeposited as a sequence of beads or layers on a substrate in an x-yplane. The extruded flowable material may fuse to previously depositedmaterial, and may solidify upon a drop in temperature. The position ofthe print head relative to the substrate is then incrementally advancedalong a z-axis (perpendicular to the x-y plane), and the process is thenrepeated to form a 3D part resembling the digital representation.

Machine 1 includes a bed 20 provided with a pair of transversely spacedside walls 21 and 22, a gantry 23 supported on side walls 21 and 22,carriage 24 mounted on gantry 23, a carrier 25 mounted on carriage 24,an extruder 61, and an applicator assembly 43 mounted on carrier 25.Supported on bed 20 between side walls 21 and 22 is a worktable 27provided with a support surface disposed in an x-y plane, which may befixed or displaceable along an x-axis. In the displaceable version, theworktable may be displaceable along a set of rails mounted on the bed 20by means of servomotors and rails 28 and 29 mounted on the bed 20 andoperatively connected to the worktable 27. Gantry 23 is disposed along ay-axis, supported at the ends thereof on end walls 21 and 22, eitherfixedly or displaceably along an x-axis on a set of guide rails 28 and29 provided on the upper ends of side walls 21 and 22. In thedisplaceable version, the gantry 23 may be displaceable by a set ofservomotors mounted on the gantry 23 and operatively connected to tracksprovided on the side walls 21 and 22 of the bed 20. Carriage 24 issupported on gantry 23 and is provided with a support member 30 mountedon and displaceable along one or more guide rails 31, 32 and 33 providedon the gantry 23. Carriage 24 may be displaceable along a y-axis on oneor more guide rails 31, 32 and 33 by a servomotor mounted on the gantry23 and operatively connected to support member 30. Carrier 25 is mountedon a set of spaced, vertically disposed guide rails 34 and 35 supportedon the carriage 24 for displacement of the carrier 25 relative to thecarriage 24 along a z-axis. Carrier 25 may be displaceable along thez-axis by a servomotor mounted on the carriage 24 and operativelyconnected to the carrier 25.

As best shown in FIG. 2, fixedly mount to carrier 25 is a positivedisplacement gear pump 74, driven by a servomotor 75, through a gearbox76. Gear pump 74 receives molten plastic from extruder 61 shown inFIG. 1. As shown in FIG. 2, a tangentially compensated bead-shapingcompression roller 59, rotatably mounted in carrier bracket 47, providesa means for flattening and leveling a bead of flowable material (e.g., athermoplastic material), as also shown in FIG. 3. Carrier bracket 47 maybe adapted to be rotationally displaced by means of a servomotor 60, asshown in FIG. 2), through a sprocket 56 and drive-chain 65 arrangement.

With continuing reference to FIG. 3, applicator head 43 may include ahousing 46 with a roller bearing 49 mounted therein. Carrier bracket 47is fixedly mounted to an adaptor sleeve 50, journaled in bearing 49. Asbest shown in FIGS. 2-3, a bead of a flowable material (e.g., athermoplastic material) under pressure from a source (e.g., one or moreextruder 61 and an associated polymer or gear pump) disposed on carrier25, to applicator head 43, may be fixedly (or removably) connected to,and in communication with nozzle 51. In use, the flowable material 53(e.g., melted thermoplastic) may be heated sufficiently to form a moltenbead thereof, delivered through applicator nozzle 51, to form uniform,smooth multiple rows of deposited material free of trapped air on tosurface 27. Such beads of molten material may be flattened, leveled,and/or fused to adjoining layers by bead-shaping compression roller 59,to form an article. Even though compression roller 59 is depicted asbeing integral with application head 43, compression roller 59 may beseparate and discrete from applicator head 43.

In some embodiments, the deposited material 53 may be provided with asuitable reinforcing material, such as, e.g., fibers that facilitate andenhance the fusion of adjacent layers of extruded flowable material 53.

In some embodiments, machine 1 may include a velocimetry assembly (ormultiple velocimetry assemblies) configured to determine flow rates(e.g., velocities and/or volumetric flow rates) of material 53 beingdelivered from applicator head 43. The velocimetry assembly preferablytransmits signals relating to the determined flow rates to theaforementioned controller coupled to machine 1, which may then utilizethe received information to compensate for variations in the materialflow rates.

In the course of fabricating a component, pursuant to the methodsdescribed herein, the control system of the machine 1, in executing theinputted program, may control several servomotors described above todisplace the gantry 23 along the x-axis, displace the carriage 24 alongthe y-axis, displace the carrier 25 along a z-axis, and rotates bracket47 about a z-axis while compression roller 59 forms uniform, smooth rowsof deposited material 52 free of trapped air to create an article.

With reference now to FIG. 4, there is illustrated a cross-sectionalschematic representation of a flowable material (e.g., meltedthermoplastic) extrusion and application system. During an additivemanufacturing process, there is a slight decompression of the depositedlayer 53, which occurs immediately after the compression roller 59passes over the bead of flowable material (e.g., melted thermoplasticmaterial). Such a decompression results in the surface of the finalflattened layer rising up, and remaining slightly higher than the bottomof the compression roller 59. This decompression is best shown FIG. 4,where distance A illustrates a difference in height between the bottomapex of the compression roller 59, and the top of the decompressedmaterial bead 53. Owing to this decompression, when the applicator head43 rotates to execute a change in tool-path direction, the edges, aswell as the outer regions, of the roller 59 tend to engage the surfaceof the final flattened layer, since it is slightly higher than thebottom apex of the roller, resulting in the roller gouging and/ordragging the deposited material during the transition.

With reference now to FIGS. 5a and 5b , the surface-contour ofcompression roller 59 can be seen in both enlarged plan views.Compression roller 59 comprises a flat center portion C for engaging andflattening the deposited bead, with the outer extremities of said rollergradually tapering to the ends in a slight elliptical curve, as shown asportions A and B in FIG. 5b . The flat surface C of roller 59 providessmooth compression and bonding of the deposited material layer, whilethe gradually-curved outer surfaces facilitates destruction-freetracking along curved portions of the deposited layer, as well as duringdirectional changes in the tool path.

In FIG. 5b , the surface features are annotated as A, B, and C fordescriptive purpose. A and B show the elliptically-tapered outersegments of the roller, while C shows the flat middle feature of theroller. The gradual outer taper of roller 59 prevents the roller 59 fromgouging and dragging molten thermoplastic material from the surface ofthe flattened layer when the roller is advanced in a non-lineardirection (e.g., when the roller turns a corner) during thestratification process, as well as when depositing and compressing abead of flowable material (e.g., melted thermoplastic) adjacent to apreviously-deposited adjoining layer, which may still be molten. Bycomparison, a completely cylindrical compression roller (e.g., a rollerwithout the tapered segments A and B depicted in FIG. 5b ) would gougeand drag the material while navigating around corners and curves, as theentire roller surface would be engaged with the slightly-decompressedand raised material surface. Compression roller 59 smooths and bonds thelayer with the flat portion of the roller, and the gradual tapering ofthe outer surfaces allows it to negotiate around the corners withoutproducing objectionable surface imperfections.

FIG. 6a , which depicts a cut-away end view of deposited strata,exemplifies the bead compression process, using the describedcompression roller 59 during the deposition of a bead of flowablematerial (e.g., melted thermoplastic) adjacent to a previously depositedand compressed bead. Tapered end 63 of the compression roller 59 doesnot substantially engage a previously deposited layer 72, and thereforehas minimal or no effect on the surface of layer 72. In someembodiments, the tapered end 63 of the compression roller 59 may betapered at both ends, as shown in FIG. 6a . In other embodiments,compression roller 59 may include only a single tapered end 63. In someembodiments, the tapered end 63 may be angled “α” approximately 1 to 15degrees relative to the surface of the center, flat portion of roller59. In some other embodiments, tapered end 63 may include a non-linearrelief (e.g., the relief is not a straight line, but a taper curvingaway from the radially outermost surface of compression roller 59).

With reference now to FIG. 6b , which is a cut-away view of stratadeposited in two directions, there is shown, an exemplary view of thecompression roller 59, executing a change of direction in the beaddeposition process. The tapered portion 63 of roller 59 does not engagethe material on the adjoining side of the article, because roller 59 isslightly tapered to prevent any substantial contact with the surface ofthat side of the deposited strata of previously deposited layers. Afterdeposition of a flowable material (e.g., melted thermoplastic) onsurface 27, as shown in FIG. 3, and while the topmost layer of depositedstrata 72, as shown in FIG. 6a , is cooling (e.g., the melted materialhas not completely solidified), compression roller 59 is used to flattendeposited strata 72 to create a uniform deposited layer. In someexamples, however, compression roller 72 must be used to flattendeposited strata 72 in a non-linear manner (e.g., when navigating acorner or curve). In such instances, compression roller 59 is used tocompress the unsolidified top-most layer of deposited strata 72, whilenavigating around the corner or curve, such that any flowable materialof the top most layer of deposited strata 72 is not gouged and/ordragged. Moreover, when roller 59 navigates a corner or curve, theroller 59 would be engaged with the slightly-decompressed and raisedmaterial surface, as previously described above.

While principles of the present disclosure are described herein withreference to illustrative embodiments for particular applications, itshould be understood that the disclosure is not limited thereto. Thosehaving ordinary skill in the art and access to the teachings providedherein will recognize additional modifications, applications,embodiments, and substitution of equivalents all fall within the scopeof the embodiments described herein. Accordingly, the inventionsdescribed herein are not to be considered as limited by the foregoingdescription.

We claim:
 1. An additive manufacturing device, the device comprising: anozzle configured to deposit a flowable material on a surface; and aroller configured to compress the deposited flowable material, whereinthe roller comprises: a flat center portion having a constant diameter;and opposed end portions, wherein each end portion extends outwardlyfrom the flat center portion, and wherein a radially outermost surfaceof each end portion is angled relative a rotational axis of the roller.2. The additive manufacturing device of claim 1, wherein the radiallyoutermost surface of each end portion extends at an angle ofapproximately 1 degree to 15 degrees away from a surface of the flatcenter portion.
 3. The additive manufacturing device of claim 1, whereineach end portion comprises a diameter that varies over a longitudinalaxis of each end portion.
 4. The additive manufacturing device of claim1, wherein the flat center portion and opposed end portions are formedintegrally.
 5. The additive manufacturing device of claim 1, wherein theradially outermost surface of each end portion tapers away from aradially outermost surface of the flat center portion and towards therotational axis of the roller.
 6. The additive manufacturing device ofclaim 1, wherein the flowable material is a thermoplastic material. 7.An additive manufacturing device, the device comprising: a nozzleconfigured to deposit a flowable material; and a roller configured tocompress the deposited flowable material, wherein the roller comprises:a cylindrical center portion having a first diameter; and opposed firstand second end portions having second and third diameters respectively,wherein the first and second end portions extend from the centerportion, and wherein the first diameter is greater than the second andthird diameters.
 8. The additive manufacturing device of claim 7,wherein the first diameter is constant over a substantial entirety ofthe cylindrical center portion, and the second and third diameters varyover the second and third end portions, respectively.
 9. The additivemanufacturing device of claim 7, wherein a radially outermost surface ofeach of the first and second end portion extends at an angle ofapproximately 1 degree to 15 degrees away from a surface of thecylindrical center portion.
 10. The additive manufacturing device ofclaim 7, wherein a radially outermost surface of each of the first andsecond end portion tapers away from a surface of the cylindrical centerportion and towards a rotational axis of the roller.
 11. The additivemanufacturing device of claim 7, wherein the cylindrical center portionand opposed end portions are formed integrally.
 12. The additivemanufacturing device of claim 7, wherein the flowable material is athermoplastic material.
 13. An additive manufacturing method, the methodcomprising: depositing a layer of a flowable material on to a surface;and compressing the layer of the flowable material with a roller,wherein the roller comprises: a flat center portion having a constantdiameter; and opposed end portions, wherein each end portion extendsoutwardly from the center portion, and wherein a radially outermostsurface of each end portion is angled relative a rotational axis of theroller.
 14. The additive manufacturing method of claim 13, wherein theradially outermost surface of each end portion tapers away from asurface of the flat center portion and towards the rotational axis ofthe roller.
 15. The additive manufacturing method of claim 13, whereinthe radially outermost surface of each end portion extends at an angleof approximately 1 degree to 15 degrees away from a surface of the flatcenter portion.
 16. The additive manufacturing method of claim 13,wherein each end portion comprises a diameter that varies over arotational axis of each end portion.
 17. The additive manufacturingmethod of claim 13, wherein the flat center portion and opposed endportions are formed integrally.
 18. The additive manufacturing method ofclaim 13, wherein the flowable material is a thermoplastic material.